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Making a probe for measurement of micronutrient level of soil in agricultural field

We are a team of students from different states with different educational background but we are going to solve a common problem which may significantly help our farmers. We are going to develop a low cost, robust and field portable sensor which can detect nutrients level in soil. Early knowledge of soil nutrient level can significantly help the farmers to use proper fertilizers on time which promotes proper growth of their crops and save there money on unneeded fertilizers.

Why to measure nutrients in soil:

Most of the famers are from rural and remote areas of India. These regions do not have any proper soil testing laboratory facility therefore, the use fertilizers on their farming fields with their experience and intuition. This would result in uneven presence of minerals in different areas therefore, different areas have different deficiencies. This leads to stunned growth of the plant. So, we are planning to develop a low cost, robust and field portable sensor/probe which can possibly help to detect the soil nutrient levels, which eventually help the farmers to add the specific nutrient required in his farm.

How minerals go/come to the soil:

Then, our team discussed how minerals come to the soil or go that are required for the plant. Or simply putting, why does farmer needs to use fertilizers. Some conclusions that we reached were :

  • Addition:

  • Due to impurities by fertilizers :

Fertilizers comes with many additional minerals in them in the form of impurities which gets added in them during their production. These impurities adds up to the mineral content of soil.

  • Artificial Addition :

For cultivation minerals are added into the soil in the form of fertilizers, pesticide, insecticide, weedicide, etc depending upon their application they are added. The quantity of addition is either intuition based or sometimes if mineral content of soil is tested than it determines the amount of mineral to be added to the soil.

  • Rock Weathering :

Formation of soil takes place from the weathering of their parental rocks so as weathering of soil takes place whether it is in the form of exfoliation or erosion of parental rock those mineral adds upto the soil.

  • Depletion:

  • due to unpresented microorganisms that are required for the growth :

If the microorganism present in soil gets killed due to some reason whether due to artificial pesticide addition or climate change. Soil looses its self mineral conversion quality as those microbes where the mineral converters, for example in the process of Nitrogen Fixation if Azotobacter bacteria gets killed than nitrogen cycle would break.

  • Due to unavailability of the specific salt of that ions that are required by the plant.

  • Due to soil erosion and exploitation :

When soil gets eroded mineral content is taken away from the soil, same is the case in leaching. If the crips gets overcrowded in a region soil in that region gets exploited and soil looses its mineral content.

Existing technologies to determine soil nutrients:

  • Electro-chemical :

  • They are field portable, in-situ measurement and quick response

  • But its calibration is difficult, requires subrogation and also different ion requires different probe.

  • Opto-chemical :

  • They have higher sensitivity and good accuracy.

  • But they are mostly lab confined and are expensive.

Developed Mind-map:

On discussion with Prof. Anil Gupta sir, we came in agreement with some points :

  • We would not be able to account all the minerals present so we should be targeting some specific minerals only.

  • Being able to achieve both accuracy and affordability would be difficult so we need to have a trade-off between accuracy and affordability.

  • Measuring the exact level would be difficult so we need to at the least, be able to tell if it is deficient on that specific mineral.

We will be visiting Amarapur village to talk to farmers regarding this problem. Then it is possible to get a clear idea of the problem statement and the exact problem faced by the farmers so that we can come up with a better solution.

A visit to farmers in Amrapur village, Mansa

May 29, 2017, Amarapur, Gandhinagar

On 29 May, we have visited a village Amarapur, near Grambharati, Gandhinagar to know the problems of our farmers regarding on time fertilization and their affects on the overall growth of crops. About 9:00 am we have reached our destination having the sun on our top. It is too hot and the farmers were working without any protection from sun then we realize the pain behind each roti.

Talk with Mr. Mahendra Rathore

When we reached in one of the farming fields, we have seen a young man is busy with his passion to feed us. We hesitate to approach him since he is working, but when he saw us waiting for him, he eventually stops. The man was Mr. Mahendra Rathore, a young man around 40 years in age. We introduced ourselves and when he knew we are from Grambharati, he became easy with us. We have asked him about the problems that he was facing in his fields. We didn’t approach the farmers with only the problems related to our problem statement instead we asked them, what problem do they expect us to solve for them. At the same time seed sowing for cotton was going on, they were sowing seed by creating a matrix through the thread the process was called hand dibbling with workers first spotting the place and then dropping 3-4 seeds at each spot. Farmer Mahendra Rathore replied that such labour-intensive process of seed sowing in farming should be replaced by affordable automated techniques. Then we asked him why he uses hand dibbling method instead of using tractor drilling methods to sow seed as that method is much faster, cheaper and requires almost no labour to which he replied that the problem is the seed spacing. Available tractor based drillers have fixed horizontal spacing and the vertical spacing adjustment is also very limited which makes seed drilling automation not useful for his required crop. He mentioned about the problem of market value for his crops. Also, he created water channels so that water can automatically spread across the field.

When we asked him about how he judged the amount of fertilizers to be used, he told us that three years ago he took five samples from five different areas of his field and went to Gandhinagar for testing with the help of Kissan Soil Card. After 10-15 days, he got the result and it said that these result were valid for 5 years. So based on that result he used the fertilizers in his field. He specifically told that he used zinc (Zn), manganese (Mn), magnesium (Mg) by dissolving it in water and circulating it in the water channels so as it reaches all the plants uniformly. When we asked why not use nitrogen (N) and phosphorus (P) fertilizers as they are major nutrients needed by the plants, he gave us a very good example to relate with. He said “ When you go to a wedding you do not eat plain rice and dal but eat something special. Similarly, nitrogen and phosphorous are something plants get regularly, we need to specially provide zinc and manganese.

Kapas (cotton) fields

We also talked to Mr. Mahendra’s brother regarding this. He also said the same thing. He also added that using too much fertilizer has never been seen as a problem to him so if he adds excess it is no problem for him. He also told that he grows bajra, juhar, kapas (cotton).

Next day, we have visited the fields of Mr. Bharat Jivan Rathore which was near to the previous fields. He also mentioned us the problem of labour -intensive process of seed sowing instead of using the tractor as he needed the proper seed spacing which was not fulfilled by tractor. We asked him about the sampling procedures that he follow, he told us that he does not sample his field soils. According to him, he just uses his own intuition and experience to apply fertilizers in the field. Mostly, he uses urea (for nitrogen) and DAP (for phosphorous). He also added that using high amounts of these fertilizers destroys the fields and since DAP is expensive, he must be careful with its usage. He said that he mostly grows beans and bajra crops.

Talk with Mr. Bhadesh Sadarji Rathore

After that we went to meet Mr. Bhardesh Sardarji Rathore, a known farmer in Amarapur. There he said that he never gave the soils for sampling since it takes time to get results from government authority. He said that he mostly uses DAP and urea, DAP would show slow effect but urea would show an immediate effect. He also said that he rarely used zinc fertilizers as he thought that it is not needed. He mentioned that he had a major problem with the attack of nilgai on their fields during night-time. So we requested the team working on the problem of warning and monitoring of the wild animals to visit them so that they can help him. He also mentioned the same problem of hand dribbling methods instead of tractor drilling methods.

We have also did a survey if every farmer we visited had a smartphone as we thought that one of our possible solution can have the need to use the smartphone. It is interesting to found that all the households carries a smartphone or at least know how to take a picture. But still the latest information and existing technology was not being used by them properly which our team was not expecting.

Problems identified :

These are the problems that our team has identified :

1) Not sampling of soil :

Most farmers do not get there soil sampled or have got there soil sampled long back and use the fertilizers based on the intution. This leads to either deficiency or excess of minerals in the soil leading to improper growth or damage to the crops. There is also the problem that once soil sampled, it is claimed to be valid for 5 years which is a very long time during which soil's content can change.

2) Usage of hand dribbling method instead of tractor drilling method:

Available tractor based drillers have fixed horizontal spacing and the vertical spacing adjustment is also very limited which makes seed drilling automation not useful for specified crops. There are very few drilling techniques and those are too seed specific and land specific, hence couldn’t be used on a larger scale. Due to this reason most seeds are still hand dibbled which consumes more labor requires expert supervision and hence makes the overall process of cultivation expensive and time-consuming. We require a “Universal Seed-Drilling Technique” that should cover the maximum possible spectrum of seeds and should allow spacing according to farmer’s requirement and should sow seed accurately independent of the speed of tractor or bullock-cart.

3) Attack of nilgai :

Many farms had a stand installed in there fields which were used at night to watch for nilgai attack. Some farmers also told us that these attacks are a regular problem in that area. So we contacted the team working with this specific problem to consult with these farmers.

Nevertheless, after this field visit our team has started to brainstorm some ideas and trying to target some selected some specific minerals only at present and finding methods to tell the deficiency of those minerals in the soil.

After successful field visit and identifying the problems, our team decided that not only micronutrients but the present farmers also need to know the value of macronutrient level in the soil. So our problem statement changed to “Finding a method to measure the nutrient level in the soil”.

Our team did some more intense prior art search through internet and also visiting SRISTI Ahmedabad office. We finalized that our first focus shall be to measure the level of Phosphorus mineral. The reason behind this was there was an easy colorimeter method based measurement technique for phosphorus already present. So, our team started working on this colorimetry method. One of our team member, Iftak did his PhD thesis on phone based spectrometer so we thought of using it to get a better reading. We thought of using camera of the phone to measure the intensity of the solution and so started working on making an app.

App to measure intensity

App to measure intensity

This spectrometer works on the principle that when light falls on the solution some light gets absorbed and then the remaining light will fall on the camera whose intensity is calculated by taking the average of all the intensities on each pixel of the camera using RGB values. A calibration graph of intensity vs concentration will be calibrated at the starting itself and as soon as intensity of sample is calculated, by comparing it with the graph, concentration of P in the soil is known.

A 3D design model of a mini-spectrometer was designed so as that it could be attached to the phone’s camera.

Small spectrometer

We got to know that a blue color solution is formed and so a red color light of nearly 660 nm would have a better absorbance in this corresponding solution. A circuit was designed and made so that it could power the red led using the phone itself.

Different intensity for different concentration

We also simultaneously worked upon the Initially, we found out an easy and already existing method in which there was just 2 steps :

  • Adding mehlich 3 soil extractment and filtering it.

  • Adding phosVer 3 powder and measure the intensity of the colour.

This method just took 10 minutes to finish. But since these chemical reagents were not available, we had to use another method which has more steps and is also needs careful handling also. In this method:

  • 5 gram of soil is digested using 2ml dilute hydrochloric acid(35-38%) and 0.3 gms of ammonium fluoride for 5minutes and then filter it.

  • Then, take 5 ml of extract and add 5 ml of ammonium molybdenum(1.5%) and dilute it with 10 ml of water.

  • Next, add 1 ml of stannous chloride and keep it stable for 5 minutes.Then, take the upper liquid and measure the absorbance of it. This will give the result.

Chemicals required

We ordered all the chemicals needed and started working on making the standard solution and our sample solution. After many trial and error to reduce the number of steps and to know the possible errors, we found out the following:

  • Never add stannous chloride and ammonium molybdenum together into the soil extract as there would be a reaction between the 2 reagents even before reacting to the extract.

  • When the final solution is formed, keep it stable and do not shake the sample. Let the precipitate get stabilize and then take the upper liquid solution for spectrometry testing.

This process poses a problem to be portable as it needs to be kept in a stable position. So, a person in a village can be trained to do the process and the farmers can reach him to test their soils.

We also are simultaneously working on an electro-chemical method in which by measuring resistance, capacitance and moisture, we can get the amount of total mineral present. By calculating this and subtracting it from the level of macronutrients found we can get an overall picture for micronutrient level. Presently, we did not make much progress so there is not much to say.

Currently, our prototype is hardware-wise ready. We have made the 3D design of the spectrometer and also the chemical processes are ready. Some work is left on the app and calibration to do before we can use it to get the results.

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